Emergent advances in adjuvant therapy for malignant bone and soft tissue tumors and the introduction of a surgical staging system to rationalize the extent and margin of tissue resection have renewed the interest in limb sparing procedures. The use of massive bone transplants to bridge defects and restore musculoskeletal joint function appears to be logical and appealing. However, previous reports and our experience all seem to indicate that there are still significant complications with such procedures, thus making results unpredictable. The underlying hypothesis of this study is that some of these complications are surgical and biomechanical in nature and that they can be minimized with better geometric matching of the graft to host bone, improved operative techniques, and specially designed fixation devices. The main goals of this project are to establish rational guidelines to select and fit allografts to host bone defects and develop an implant system tailored to various reconstructive methods at different anatomic regions. To accomplish these goals, we propose: 1) to study major long beon geometry based on biplanar contact radiography and CT scan to identify key dimensional parameters for proper selection of size ranges for the implants and for optimal fit of osteochondral grafts at the knee; 2) to perform both 2-D and 3-D computer simulation on osteochondral graft reconstruction for the knee joint based on weight-bearing AP x-ray and CT scan in order to achieve ideal joint contact pressure distribution; 3) to develop a system of interchangeable modular implants with porous coating to accommodate massive autogenous bone graft fixation requirements; 4) to validate the efficacy of these new fixation devices based on bench tests and animal experiments; and 5) to evaluate patients with different reconstructive procedures for similar tumor resections for the purpose of comparing their clinical results, functional deficits, extent of autogenous graft donor site morbidity, and personal satisfaction. The results of these studies are expected to improve the clinical outlook of autograft and allograft transplantations for the reconstruction of skeletal defects in carefully selected cases. The surgical techniques and fixation devices developed here will also benefit other orthopedic procedures involving extensive bone and joint defects.